<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>清除内外边距</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
    </style>
</head>

<body>
    123
    <ul>
        <li>opql</li>
    </ul>
</body>

</html>